1. Technical Field
This invention relates to the field of reinforced tubing for medical applications. More particularly, the invention relates to a method of forming reinforced tubing, and to tubing formed by the inventive method.
2. Background Information
Numerous advances of considerable note have occurred in medical surgical techniques over the last few decades. Among the most significant advances has been the adoption, and now-routine performance, of a variety of minimally invasive procedures. Such procedures include angioplasty, endoscopy, laparoscopy, and arthroscopy, as well as numerous other diagnostic and therapeutic operations. These minimally invasive procedures can be distinguished from conventional open surgical procedures in that access to a site of concern within a patient is achieved through a relatively small incision, into which a tubular device (e.g., an introducer sheath) is inserted or introduced. The tubular device, or device portion, keeps the incision open while permitting access to the target site via the interior (i.e., the lumen) of the device.
Body passageways in which introducer apparatuses have been used to introduce medical interventional devices and/or liquid medicaments include the esophagus, trachea, colon, biliary tract, urinary tract, and virtually all portions of the vascular system, among others. One common example of a minimally invasive technique involves the temporary or permanent implantation of a medical interventional device, such as a stent, into a body passageway of a patient. Other examples involve the transmission of a liquid medicament to a target area, and/or the withdrawal of body fluid from the body passageway.
When carrying out these, and other, desired techniques, communication with the passageway is typically attained by inserting a tubular access device, such as an introducer sheath, into the body passageway. One typical procedure for inserting the introducer sheath is the well-known Seldinger percutaneous entry technique. In the Seldinger technique, a needle is initially injected into the passageway, such as a vessel, and a wire guide is inserted into the vessel through a bore of the needle. The needle is withdrawn, and an introducer assembly is inserted over the wire guide into the opening in the vessel.
Typically, the introducer assembly includes an outer introducer sheath, and an inner dilator having a tapered distal end that extends beyond (i.e., distal to) the distal end of the introducer sheath. The tapered end of the dilator stretches the opening in the vessel in controlled fashion, so that introduction of the larger diameter introducer sheath may then be carried out with a minimum of trauma to the patient. Following satisfactory placement of the introducer sheath, the dilator is removed, leaving at least the distal portion of the larger diameter introducer sheath in place in the vessel. The medical interventional device, e.g., a stent, or a liquid medicament may then be passed through the introducer sheath for delivery to the target site.
Historically, percutaneous insertion techniques were problematic, due in large part to the lack of flexibility and/or kink resistance of the sheath. Early sheaths were generally formed of a relatively stiff fluoropolymer, such as polytetrafluoroethylene (PTFE) or fluorinated ethylene propylene (FEP). The sheaths were typically of thin-walled construction, and were prone to kinking, particularly when threaded through tortuous pathways within the body. Increasing the thickness of the sheath only minimally improved the kink resistance of the sheath. At the same time, the added thickness occupied valuable space in the vessel, thereby minimizing the diameter of the interventional device that could be passed therethrough. In addition, increasing the thickness of the sheath necessitated the use of a larger entry opening than would otherwise be required.
A kinked sheath is essentially unusable, and generally cannot be straightened while positioned in the body of the patient. Consequently, once a sheath kinks, the sheath must be removed, leaving an enlarged, bleeding opening which typically cannot be reused. Access to the vessel must then be re-initiated at an alternative site, and the process repeated with a new sheath. In some cases, a suitable alternative site is not available, and the percutaneous procedure must be abandoned altogether in favor of a different, and often more intrusive, technique.
In recent years, introducer sheaths have been improved in order to enhance their flexibility and kink resistance. Such sheaths are now routinely used to percutaneously access sites in the patient's anatomy that previously could not be accessed with existing sheaths, or that could be accessed only upon the exercise of an undesirable amount of trial and error, with the concomitant discard of sheaths whose placement had been unsuccessful. One example of a flexible, kink resistant introducer sheath is described in U.S. Pat. No. 5,380,304. The sheath described in this patent includes a lubricious inner liner having a helical coil fitted over the liner. A polymeric outer jacket, e.g., a polyether block amide, a polyamide (e.g., nylon), or urethane, is fitted over the coil and liner. The entire assembly is then typically placed in a heat shrink enclosure, and subjected to sufficient heat to melt the outer jacket. The melted outer jacket bonds to a roughened outer surface of the liner through the coil turns. The coil reinforcement imparts kink resistance to this thin-walled sheath through a wide range of bending.
U.S. Patent Publication No. 2001/0034514 discloses an introducer sheath similar in many respects to the sheath of the '304 patent. The sheath in the patent publication is formed such that the proximal end of the sheath has a higher stiffness, while the distal end has a lower stiffness. Since the distal portion of the sheath has a lower stiffness (and therefore is more flexible) than the proximal portion, the sheath is able to traverse portions of the anatomy that would have been difficult, if not impossible, to traverse with stiffer sheaths. Since the proximal portion has a higher stiffness (and is therefore less flexible) than the distal portion, the sheath maintains sufficient trackability to traverse tortuous areas of the anatomy. This presence of the coil reinforcement also enables this sheath to be kink resistant through a wide range of bending angles.
The development of introducer sheaths, such as those described above, has revolutionized the practice of medicine. In particular, these advances have enhanced the ability of the physician to introduce medical interventional devices and liquid medicaments into target sites that had previously been difficult, if not impossible, to reach without the necessity of carrying out much more intrusive open surgical operations. The percutaneous methods described are generally less expensive than the open surgical methods previously employed, are less traumatic to the patient, and typically require a shorter patient recovery time.
In many introducer sheaths, such as the sheaths described in the incorporated-by-reference patents, the lubricious inner liner may be formed of PTFE. PTFE is advantageous because it provides a slippery, low friction inner surface to ease insertion and/or withdrawal through the sheath passageway of a dilator or a medical interventional device, such as a stent. PTFE also has high chemical resistance and inertness, and low thrombogenicity. However, due to this chemical resistance and inertness, PTFE does not bond particularly well with other polymers, such as the polymeric materials used for the outer jacket of the sheath.
Sheaths such as those described above have been well-received in the medical community. These sheaths have greatly enhanced the ability of the physician to utilize less traumatic percutaneous procedures in situations wherein open surgical procedures may have been previously required. Notwithstanding the benefits that have been achieved by the use of such introducer sheaths, new challenges continue to be faced. For example, preparation of such sheaths is a highly labor intensive operation. The sheaths must be individually prepared, generally by hand, wherein one sheath at a time is assembled, and melted as described. This results in an expensive product, which increases the cost of the medical procedure. This cost is increased even further if more than one sheath is necessary in order to accomplish a particular procedure. In addition, due to the general chemical inertness and lack of reactivity of the PTFE liner, the strength of the bond between the PTFE and the outer polymeric layer may be less than optimal. This may result in a higher percentage of rejects during the manufacturing process than desired. This, of course, also increases the cost of the medical procedure.
It is desired to provide a method of forming a reinforced tubular member that overcomes the problems of the prior art. It is also desired to provide a tubular member formed by the inventive method.